The present invention is related to a method of preparing cement clinker from carboniferous shale or from any mineral substance capable of releasing a certain amount of calorific power.
The invention also relates to a cement making installation, for carrying out the above method, said installation being adapted to utilize a starting material which may contain calcareous carboniferous shale issuing from a lignite mine washing installation.
The installation according to the invention is also adapted to operate temporarily with conventional cement making starting materials.
Tests and measurements carried out on such types of substances capable of releasing a certain amount of calorific power have shown that these substances have generally a comparatively low starting combustion temperature, in the order of 200.degree. C., and that they release at a comparatively low temperature tars and distillation products liable to condensate at about 400.degree. C. The quality of these products furthermore is quite inconsistent and they may contain large amounts of sulphur, which is undesirable in that the latter interfere with the normal conditions of preparation of cement clinker.
In the method according to the invention, a raw material is clinkerized which is constituted, in part, by previously calcined carboniferous shale and in part by additive substances comprising clay, limestone and, possibly, other additive substances, which additive substances of the raw material are previously at least partially decarbonated.
The present invention is also related to an installation for carrying out the method of treating the shale.
In fact, the adding of the above-mentioned additive substances is effected depending on the composition of the shale used.
Said installation comprises a rotary clinkerization kiln and a cooler, an exchanger column with staged cyclones which is provided with a fuel injection pre-calcinator, and a shale treating column comprising staged cyclones and a calcination reactor, said exchanger column being fed only with the additive substances of the raw material and effecting the partial decarbonation thereof, while receiving the gases issuing from the cooler, whereas the shale treating column effects the calcination of said shale or of a mixture of shale with at least one additional substance prior to the introduction thereof into the kiln, said shale treating column being fed with the fumes issuing from the kiln and comprising two dust recirculation circuits provided, respectively, between the upper cyclone fed with fumes issuing from the third cyclone from above the cyclone located immediately beneath, which is fed with cool air, and between the lowermost cyclone fed with cool air and the cyclone located immediately above which is fed with the gases issuing from the kiln and the calcination reactor. This arrangement of the cyclones is disclosed in French Patent Application No. 78 01 337 filed in the name of the Applicant.
Whenever the circulating dust loads prove insufficient, it is possible to feed these two circuits with a powderous or granular material the nature of which depends on the chemical composition of the fumes.
Preferably each one of said columns comprises four cyclone stages.
In one embodiment of the invention the gases issuing from the kiln are at least partially by-passed and are quenched by adding cool matter which circulates in the installation and is submitted to a heat exchange with cool air.
During treatment, the shale is injected, possibly with an addition of fuel, into the fumes conduit of the lowermost cyclone of the treating column, which opens into the calcination reactor, the outlet of the latter opening into the kiln, while at least a portion of the dust issuing from the lowermost cyclone is introduced into the fumes conduit of the kiln and partially evacuated. The amount of the fuel possibly introduced together with the shale depends on the calorific power of the latter.
According to one feature of the above-mentioned installation at least a portion of the dust issuing from the second cyclone from above of the shale treating column is injected into the fumes conduit of the lowermost cyclone upstream of the point of injection of the shale.
According to the invention, the hot gases issuing from the zone of treatment of the shale are used for producing energy, especially in the form of steam.
For this purpose the hot gases of the two upper cyclones of the column are introduced, respectively, into the two stages of a two-stage exchanger.